Magnetic materials



United States Patent Office,

3 1 3,3,6'2 Patented July 6, 1965 3,193,362 MAGNETIC MATERIALS Wilbur G. Hespenheide, Malvern, 9a., assignor to Burroughs Corporation, Detroit, Mich, a corporation of Michigan No Drawing. Original application Sept. 25, 1958, Ser. No. 763,169, new Patent No. 3,947,475, dated Early 31, 1962. Divided and this application Nov. 22, 1961, Ser- No. 154,329

6 Claims. (Cl. 29191.6)

This application is divided from the co-pending United States application for patent entitled Magnetic Materials, Serial No. 763,169, filed September 25, 1958, now Patent No. 3,047,475, granted July 31, 1962. This invention relates to coated electrical conductors and more particularly to a substantially continuous tightly adherent magnetic coating on a relatively rough surfaced electrical conductor.

In the construction of static magnetic binary information storage devices, it hasbeen found advantageous to employ rods or wires coated with magnetic material having a substantially rectangular magnetization curve, and 'having a predetermined coercive force. Plates or layers of such material may also be employed for information storage; :and the use of magnetic materials of rectangular magnetic characteristics is common for so-called magnetic amplifiers. The electrical arts in general make wide use bf ferromagnetic materials of various magnetic, physical, :and geometric properties. Electrodeposition is a particularly convenient method of fabrication of metal parts,

but its application to the production of magnetic cores for commercial purposes has not been commensurate with the use of electrodeposition in industry for other purposes, such as protective coatings; this reflects the difficulty of controlling by the presently known art the magnctic properties, particularly the coervice force, of coatings thus deposited. While in some applications of magnetic materials, the coercive force does not matter providing it does not exceed some particular magnitude, in certain other uses, such :as coincident current memories, it must be held between certain relatively close maximum and minimum values. My present invention specifies :a magnetically coated electrical conductor produced by electroplating iron-nickel alloys so as to produce closely controlled magnetic properties, particularly coercive force. (Coercive force will be specified in oersteds throughout this specification.)

The desirable range of coercive force of magnetic material, especially for information storage, is determined by the lower bound that it should exceed any expected stray fields by a sufficient amount that its operation will not be affected by the stray fields; and by the upper bound,

that the coercive force required to switch it from one to another state of magnetization should not be so great that the power dissipated in it and the currents required to produce the requisite magnetomotive force gradient in it are inconveniently large. Obviously, the design of the particular equipment employing the magnetic material will itself determine some of the parameters which determine these bounds. In general, however, desirable coparameters whose control is necessary or beneficial to obtain desired products are:

Concentration of iron sulfarnate Concentration of nickel sulfamate Concentration of hydrogen ions, or pH Current density at cathode Bath temperature In producing materials of particularly low coercive force, annealing of the final product may be ane cessary additional step, as will be further described.

Accordingly an object of my invention is to provide an electrical conductor having a magnetic coating wherein the magnetic coating has closely predictable magnetic properties, particularly coercive force.

Another object of my invention is to provide a magnetic coating on an electrical conductor having a relatively rough surface.

A further object of my invention is to provide a nickeliron magnetic coating of predictable magnetic properties on an electrical conductor having a surface roughness of at least two microinches R.M.S.

A still further object of my invention is to improve magnetic coated conductors.

These and other objects of my invention are accomplished by electrodepositing a magnetic nickel-iron alloy on an electrical conductor such as a stretched copper wire. The stretched copper wire has a surface rough ness of at least two microinches R.M.S. and is utilized as a cathode in a Water solution bath of iron and nickel sulfate. The anode comprises a soluble nickel or nickeliron alloy. The parameters of the electrodepositing operation( such as current density, bath temperature etc.) are varied to vary the coercive force of the magnetic coating. Heretofore in the prior art nickel-iron magnetic coating have been limited to a low coercive force and have been limited to substrates having an extremely smooth surface as reported by Wolf, Katz, and Brain, page 15, Proceeding of Electronics Components Conference, Philadelphia, Pennsylvania, May 6-8, 1959.

"the bath 'I employ in producing my invention is an aqueous solution of nickel sulfamate and iron sulfamate which is rendered acidic by the addition of sulfamic acid. The magnetic coating whose production is an object of the invention is deposited upon an electrode which is the cathode. The anode is preferably of soluble nickel or nickel-iron alloy. If the anode does not replace by its solution the material deposited from the bath on the cathode, corresponding salts must be added to the bath to maintain its composition at the desired value. Thus, the

ercive forces for many uses range from a few tenths of e an oersted to fifty or a hundred oersteds.

The art of electroplating is, for one of the electrical arts, extremely old and, despite its relative antiquity, because it deals with materials, and particularly with materials in the solid form, and with the boundaries between different solid materials, tends to bevery much an art. The parameters in electroplating are numerous and susceptible of wide variation, with interdependent effect.

The bath employed in the practice of my invention is a water solution of iron and nickel sulfamates. The

use of a pure nickel anode when nickel-iron alloy is being deposited would require the addition to the bath of iron sulfamate to replenish the iron content. Operation such as described, where the depletion of the metallic content of the bath is not completely compensated by replenishment by anode solution will cause the pH of the bath to decrease. It may be adjusted upward by the addition of nickel carbonate which will also increase the nickel content of the bath, but not to an objectionable extent in the amounts required for pH adjustment.

In reducing this invention to a practical form, I have made numerous experiments, whose results are a part of the teaching of my invention. I therefore present in tabular form the results which I found for ditferent concentrations of ionic iron, different concentrations of ionic nickel, different degrees of acidity or hydrogen-ion concentration (expressed in unit of pH, conventional in the chemical and electrochemical art), difierent bath temperatures, and different densities of plating current at the cathode. All depositions were one thousandth of an inch thick and were made on copper wire which had been 7 9 stretched cold to a percent increase in length (and thus presumably a 5 percent reduction in cross section) from an initial annealed state. Stretched copper wire inherently has a surface roughness of at least two (2) microinches R.-M.S. as is disclosed in tables and publications made available by wire manufacturing concerns. The metallographic structure of the nickel-iron magnetic coating is characterized by the fiber axis being normal to the surface of the electrical conductor. This orientation is inherent in electrodepositing when there is no further annealing and is more fully discussed on pages 514515 of a text titled Metallurgy and Metallurgical Engineering Series by Charles S. Barrett, Ph.D., second edition, McGraw- Hill Book Company 1952. The tables presented here-inafter are here listed for convenient reference.

Table 1.Coe;rcive force of coating as deposited, coercive force of coating after annealing, and percent iron in the deposit, for a bath containing 25 grams per liter of iron as ferrous ion and 77 grams per liter of nickel as nickelous ion, for current densities from 0.17 to 5.0 amperes per square inch, for temperatures from 70 to 195 degrees Fahrenheit, and a pH of 1.7. r

I Table 2. The same data as in Table l, for the same bath, the same current densities, and for temperatures from 100 to 195 degrees Fahrenheit, but fora pH of 2.5.

Table 3.--Coercive force of coating as deposited, coercive force of coating after annealing, and percent iron in the deposit, for a bath containing 49 grams perlit-er of iron as ferrous ion and 64 grams per liter of nickel as nickelous ion, for current densities from 0.17 to 5.0 ampere-s per square inch for temperatures from 70 to 195 degrees Fahrenheit, and a pH of 1.7.

Table 4.-The same data as in Table 3, for the same bath, the same current densities, and for temperatures from 100 to 195 degrees Fahrenheit, but for a pH of 2.5.

Table 5 .Coercive force of coating as deposited, coercive force of coating after annealing, and percent iron in the deposit, for a bath containing 100 grams per liter of iron as ferrous ion and 39 grams per liter of nickel as nickelous ion, for current densities from 0.17 to 5.0 amperes per square inch, for temperatures from 70 degrees Fahrenheit to 195 degrees Fahrenheit, and a pH of 1 .7.

Table 6. The same data ,as in Table 5, for the same bath, the same current densities, and for temperatures from 100. to 195 degreesFahrenheit, but for a pH of 2.5

Table 7 .-Coercive force of coating as deposited, coercive force of coating-after annealing, and percent iron in the deposit, for a bath containing 149 grams per liter of iron as ferrous ion and 13 grams per liter of nickel as, nickelous ion, for current densities from 0.17 to 5.0 amperes per square inch, for temperatures from 70 to 195 degrees Fahrenheit, and a pH of 1.7.

Table 8.-The same data as in Table 7, for the same bath, the same current densities, and for temperatures from 100 to 195 degrees Fahrenheit, but fora pH of 2.5

Table 9.--Coercive force of coating as deposited, coercive force of coating after annealing, and percent iron in the deposit, for a bath containing 12 grams per liter of iron as ferrous ion and 39 grams per liter of nickel as nickel-ous ion, for current densities from 0.17 to'5.0 amperes per square inch, for temperatures from 100 to 195 degrees Fahrenheit, and a pH of 1.7.

Table 10.--The same data as in Table 9, for the same bath, the same current densities, and the same temperatures, but for a pH of 2.5.

Table 11.,Coercive force of of iron as ferrous ion and 32 grams per liter of nickel as nickelous ion, for current densities from 0.17 to 5 .0 amperes per square inch, for temperatures from 100 to 195 degrees Fahrenheit, and a pH of 1.7.

Table l2.-The same data as in Table 11, for the same bath, the same current densities, and the temperatures, but for a pH of 2.5.

coating as deposited, coercive force of coating after annealing, and percent iron. .in the deposit, for a bath containing 25 grams per liter Table 13.-Coercive force of coating as deposited, coercive force of coating after annealing, and percent iron in the deposit, for a bath containing 50 grams per liter of iron as ferrous ion and 20 grams per liter of nickel as nickelous ion, for current densities from 0.17 to 5 .0 amperes per square inch, for temperatures from to 195 degrees Fahrenheit, and a pH of -1.7.

Table 14.-.T:he same data as in Table 13, for the same bath, the same current densities, and the same temperatures, but for a pH of 2.5.

Table 15.'Coer-cive force of coating as deposited, coercive force of coating after annealing, and percent iron in the deposit, for a bath containing 74 grams per liter of iron as ferrous ion and 6 grams per liter of nickel as nickel'ou-s ion, for current densitiesfrom 0.17 to 5.0 arnperes per square inch, for temperatures from 100- to 195. degrees Fahrenheit, and a pH of 1.7.

Table 16.-The same data as in Table 15, for the same bath, the same current densities, and the same temperatures, but for a pH of 2.5.

Key to tables: Since three ditferent kinds of information are included in a single table, to avoid excessive repetition of captions the information is given according to a positional key. The coercive force before annealing is placed on a first line;'the iron content is placed on the next line below, and to the right; and the coercive force after annealing is placed another line below, and still further to the right. Thus, for example, in Table 2, the first entries are:

This signifies that at a current density of 0.17 ampere per square inch and a :bath temperature of 100 degrees Fahrenheit, a deposit was produced which had a coercive force before annealing of13 oersteds, an iron content of 51 percent, and a coercive force after annealing of 7 oersteds. At the same cur-rent density, but at a temperature of degrees Fahrenheit, a deposit was produced with 3.7 oersteds coercive force before annealing, an iron content of 6.1 percent, and a coercive force after annealing of 6 oersteds. This presentation method is believed preferable to the presentation of three times the number oftables actually included herein.

, Table 1 I Bath: Iron 25 gramsper liter, nickel 77 grams per liter, pH 1.7

T able 2 Table 5 Bath Iron 25 grams per liter, nickel 77 grams per liter, pH 2.5 Bath: Iron 106 grams per liter, nickel 39 grams per liter, pH 1.7

Temperature, deg ees F. Temp degrees Current density, Current deqsity,

amps-lsq' 100 150 195 m 70 100 150 195 11 3. 6 1O 1O 25 l. 7 0. 42 45% 49% 50% 0.42 86% 85% a Table 3 T able 6 Bath: Iron 49 grams per liter, nickel 64 grams per liter, pH 1.7 Bath: Iron 100 grams per liter, nickel 39 grams per liter, pH 2.5 Current den- Temperature, degrees F. Temperature, degrees F. sity, agnpsJ 30 Current den 1ty,

70 100 150 195 amPSJsq- 100 150 195 2. 5 1. 6 3 6 7 10. 5 3. 9 9 11 V 3. 8 11. 5 U. 83 77% 76% 50% 0. 83 V 96% 87% 83% Table 4 Table 7 Beth: Iron 49 grams per liter. nickel 64 grams per liter, pH 2.5 Bath: Iron 149 grams per liter, nickel 13 grams per liter, pH 1.7

Temperature, degrees F. Temperature, Degrees F. Current deneity, Current deneity,

100 150 195 amps-1S2 S 4. 5 3. 5 4 1 2. 5 12 4. 2 5. 5 65 so 1. 9 13 1. 67 76% 79% 59% 1. 67 97% 96% 97% .Table 8 Table 11 Bath: Iron 149 grams per liter, nickel 13 grams per liter, pH 2.5 Bath: Iron 25 grams periiter, nicke132 grams per liter, pH 1.7

Temperature, degrees F. V 7 Temperature, degrees F. Current/density, C t d t amps. sq. 1n. urren ensi y,

100 .150 195 amps /Sq m 100 150 I 195 13 4. 8 5. 5 9 3 2. 4 Table 9 Table 12 Beth: Iron 12 grams per liter, nickel 39 grams per liter, pH 1.7 Bath: Iron 25 grams per liter, nickel 32 grams per liter, pH 2.5

a Temberature, degrees F. Temperature, degrees F. Current density amps/sq. in. I Current density,

100 150 j 195 amPi/Sq- 100 150 195 1s 1. 7 17 V 9 6 15 0. 17 55% I 44% 0. 17 73% 47% 6. 6 2. 4 4. 5 50 10.5 6. 9 7. 5 Table 10 7 Table 13 Bath: Iron 12 grams per liter, nickel 39 grams per liter, pH 2.5 Bath: Iron 50 grams per liter, nicke1 20 grams per liter, pH 1.7

Temperature, degrees F. Temperature, degrees 13. Current density, 7 Current density,

ampsJsq. 1n. 100 150 195 V amps/sq. 1n. 100 150 195 Table 14 Current density,

Temperature, degrees F.

amPSJSL 100 150 195 Table 15 Bath: Iron 74 grams per liter, nickel 6 grams per liter, pH 1.7

Temperature, degrees F. Current density, amps] Table 16 Bath: Iron 74 grams per liter, nickel 6 grams per liter, pH 2.5

Current density, amps/sq. in.

Temperature, degrees F.

Reference to Tables 1 through 16, inclusive, reveals that a large range of values of coercive force may be obtained by varying the parameters of the plating operation. Specifically, values from less than one oersted to over one hundred oersteds are obtainable. Although annealing is generally expected according to the art to produce a reduction in coercive force, annealing unexpectedly produccd an increase in approximately as many cases as it produced a decrease in coercive force. The annealing process employed in the production of my invention, where annealing is a step in obtaining the desired properties may consist of heating for three hours at 300 degrees centigrade in hydrogen. This is not critical; the time and the temperature are adequate to produce the desired effect, and the hydrogen is a preventive of oxidation of the metal deposit. Other, more drastic annealing treat ments may be found desirable for certain materials and applications. One trend which appears, from a study of the data, is that a temperature of 150 degrees Fahrenheit and a pH of 1.7 is favorable to the production of a low coercive force in the annealed material, particularly for a middle range of current densities listed. As a specific example, Table 3 for current density of 2.5 amperes per square inch and a temperature of 150 degrees Fahrenheit, 49 grams per liter of ferrous ion and 64 grams per liter of nickelous ion, at a pH of 1.7 shows a coercive force after annealing of 0.1 oersted. This is one preferred mode of operation of my invention, to obtain low coercive force material after annealing.

Table 3 indicates that for current density of 1.67 amperes per square inch and a temperature of 195 degrees Fahrenheit, 49 grams per liter of ferrous ion and 64 grams per liter of nickelous ion, at a pH of 1.7 a deposit is obtained Whose coercive force before annealing is oersteds. This is a mode of operation suitable for producing relatively high coercive force; and the required conditions dilfer surprisingly little from those for low coercive force.

However, since the problem of controlling the parameters of a plating operation is sometimes burdensome, especially in large scale production operations, it is desirable to select an operating point such that small departures from the selected values of parameters will not produce a very great change in the result obtained. Thus reference to Table 18 indicates that for a current density of 1.67 ampercs per square inch, a temperature of degrees Fahrenheit, 5 grams per liter of ferrous ion and 77 grams per liter of nickelous ion, at a pH of 2.5, a deposit will be obtained with a coercive force of the order of 100 oersteds, and small changes in current density will have only slight influence on the result.

I have found in the course of my tests that a practical upper limit for the pH of nickel and iron sulfamate plating baths is pH equal to 4, since a higher pH value tends to permit precipitation of hydroxides of iron, which is undesirable both because it arbitrarily changes the bath composition, and produces a mechanical contaminant in the bath. While I conducted the tests Whose results are included in the tables at a minimum pH of 1.7, I have found that it is possible to employ lower values of pH, but for this purpose it is necessary to increase the current density to obtain an equivalent result. Thus it appears that for the most convenient and best operation of my invention, a value of pH not less than 1.5 nor more than 4 is preferable. Similarly, a temperature range between usual room temperature and the boiling point of the bath is preferable.

I have also found in the course of my tests that iron tends to be deposited more readily from the nickel and iron sulfamate bath than does nickel. Thus apparently the layer of electrolyte next to the cathode tends to become depleted of iron first, especially if the concentration of iron is small relative to that of nickel. To keep the percentage of iron in the deposit constant with an increase in current density, it is necessary to increase the 3 1 7 concentration of iron in the bath. An increase in bath temperature, presumably by increasing the rate of diffusion of iron from the rern'oter parts of the bath toward the depleted layer next the cathode, has an effect similar to that of increasing the iron concentration.

The correlation between the composition of the deposit and its magnetic properties is very vague at best; this is assumed to be due to the known large effect of internal stresses upon the magnetic properties. Thus the magnetic properties are not predictable by the application of any art which might propose to predict composition of the deposit.

Obviously many modifications and variations of the present invention are possible in the light of the above 7 teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced other than as specifically described and illustrated.

\Vhat is claimed is:

1. A magnetic circuit device comprising a magnetic material deposited on a cold-stretched, nonmagnetic, electrical conductor, said magnetic material possessing a magnetic hysteresis loop exhibiting a coercive force requirement of less than three oersteds, said magnetic material so deposited having a metallographic structure in which the fiber axes of said magnetic material are normal to the surface of said electrical conductor.

2. The magnetic circuit device as set forth 'in claim 1 wherein said magnetic material possesses a substantially square magnetic hysteresis loop.

3. A magnetic circuit device comprising a magnetic material electrodeposited on a cold-stretched nonmagnetic, electrical conducting wire, having a surface roughness of greater than 2 microinches, R.M.S., said magnetic material possessing a magnetic hysteresis loop exhibiting a coercive force requirement of less than three oe'rsteds, said electrodeposited magnetic material having a metallographic structure in which the fiber axes of said maga coercive force requirement of less than three oersteds netic material are normal to the surface of said conducting wire. I

and further possessing a metallographic structure in which the fiber axes of said electrodeposited magnetic material are normal to the surface of the electrical conductor, said magnetic deposition being capable of division into a plurality of adjoining circumferential segments lengthwise along said conductor, each segment being capable of directional magnetization in the corresponding polarized direction of an applied polarized electrical signal to said segment, said signal alternately having an oppositely polarized value exceeding said coercive force, whereby the magnetized condition of each of said plurality of circumferential segments represents the corresponding signal applied to said segment, said device thereby magnetically recording and storing the polarized direction of each said applied signal along said conductor.

6. The recording and storage device set forth in claim 5 wherein said nonmagnetic conducting material is a cold= stretched, substantially circular copper wire.

References (Iited by the Examiner UNITED STATES PATENTS 1,140,136 5/15 Eldred.

1,527,177 2/25 Elmen 14831.55'X 1,586,884 6/26 Elmen -170 X 1,679,518 8/28 Fowle 29l96.3 X

1,718,946 7/29 Casper 7517O X' 1,762,730 6/30 McKeehan 1 48--31.55 X 1,902,621 3/33 Davis 29-191 2,682,702 7/54 Fink.

2,858,520 10/58 Chance.

DAVID L. RECK, Primary Examiner.

HYLAND BIZOT, Examiner. 

1. A MAGNETIC CIRCUIT DEVICE COMPRISING A MAGNETIC MATERIAL DEPOSITED ON A COLD-STRETCHED, NONMAGNETIC, ELECTRICAL CONDUCTOR, SAID MAGNETIC MATERIAL POSSESSING A MAGNETIC HYSTERESIS LOOP EXHIBITING A COERCIVE FORCE REQUIREMENT OF LESS THAN THREE OESTEDS, SAID MAGNETIC MATERIAL SO DEPOSITED HAVING A METALLOGRAPHIC STRUCTURE IN WHICH THE FIBER AXES OF SAID MAGNETIC MATERIAL ARE NORMAL TO THE SURFACE OF SAID ELECTRICAL CONDUCTOR. 